Although a number of studies of transgenic animals made with constructs of the amyloid precursor protein (APP), C-terminal 99 or 1 amino acids (C-99,-1), or beta-amyloid protein (A-beta), have been reported, these animals, to date, have not developed the brain abnormalities characteristic of Alzheimer's disease (AD). A difficulty with most of these studies, all of which utilized cDNA constructs, has been the very low levels of expression of the transgene products. Moreover, there are, as of yet, no published studies that describe animals created by introduction into the mouse germline of transgenes with APP mutations linked to early-onset familial AD (FAD) or hereditary cerebral hemorrhage with amyloidosis, Dutch type (HCHWA-D). We have used yeast artificial chromosome (YAC) and embryonic stem (ES) cell technologies to introduce about 450 kilobases of the human APP gene into mice; these transgenic animals express the wild-type transgene at the level of the endogenous APP gene. In this Project, these strategies will be used to produce transgenic animals with APP mutations linked to FAD or to HCHWA-D, chosen because these mutations were chosen because, in humans, they are linked to early-onset illnesses with distinct phenotypes. To delineate the character/evolution of the pathology, we will examine controls and lines of transgenic mice with a variety of approaches to identify preamyloid deposits, plaques, congophilic angiopathy, abnormalities of the neuronal cytoskeleton, alterations in neural circuits, and synaptic pathology. We will focus on the early stages of A-beta formation, the cells participating in these processes, and using stereological methods, the possibility that animals will show age-related reductions in the numbers of synapses in hippocampus and cortex. Using invasive methods, APP will be radiolabeled by injecting [35S] methionine into the entorhinal cortex, and the transport and processing of APP will be examined in the perforant pathway. Transgenic animals developing brain abnormalities will be extraordinarily valuable for investigations designed to test diagnostic and therapeutic strategies relevant to FAD, HCHWA-D, or AD.